Disposable ballpoint pens are well known in the art. One common version, known as a "stick pen", includes a combined tip/ink supply which is press fit into one end of a housing. Such pens generally include a cap member to cover and protect the writing tip during periods of non-use. When the pen is to be used, the cap is removed and placed on the opposite end of the housing. It is also typical for such cap members to include an integral clip for attachment to the pocket of the user during periods of non-use. The storage of the pen in an "upside down" position sometimes results in leakage of ink into the pocket of the user, while the cap members are often lost or discarded.
Retractable pens are also known in the art. These pens usually include two molded body components--a replaceable ink cartridge, and an internal extension/retraction mechanism. The body components are generally joined by mating threads to provide easy access to the interior of the pen, primarily for replacement of the cartridge after the ink is depleted. Such pens are generally more expensive than the stick pens, and can be continuously used by merely replacing the ink cartridge. One example is disclosed in U.S. Pat. No. 3,288,115 to Hechtle.
At present, however, an inexpensive disposable stick pen which includes a mechanism for extending and retracting the writing cartridge to facilitate use and storage while avoiding unwanted transfer of ink from the writing point, as by transfer to a garment pocket, for example, does not exist. We have invented such a writing instrument.